Reticles with subdivided blocking regions

ABSTRACT

Methods for designing, fabricating, and using attenuated phase shift reticles, or photomasks are disclosed. Methods are also disclosed for subdividing the radiation blocking regions of previously fabricated reticles of previously existing designs. The methods may include forming radiation blocking regions that are subdivided, by cut lines, into discrete, spaced apart sections with dimensions (e.g., surface area, etc.) configured to minimize or eliminate the buildup of electrostatic energy by the radiation blocking regions and/or the discharge of electrostatic energy from the radiation blocking regions and the damage that may be caused by such electrostatic discharge. The methods may include configuring the reticle to prevent radiation from passing through the cut lines between adjacent sections of a subdivided radiation blocking region.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/305,987, filed Nov. 29, 2011, pending, which is a continuation ofU.S. patent application Ser. No. 12/265,518, filed Nov. 5, 2008, nowU.S. Pat. No. 8,071,262, issued Dec. 6, 2011, the disclosure of each ofwhich is hereby incorporated herein by this reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to reticles, which are alsoreferred to in the art as “photomasks” and, more specifically, toreticles with light blocking layers that are configured to minimize thebuildup and/or discharge of electrostatic energy. Specifically,embodiments of the present invention relate to reticles that includelight blocking layers that are split into discrete, spaced apartsections, each having an area that minimizes the buildup and/ordischarge of electrostatic energy.

BACKGROUND

Reticles are masks that are used to control the portions of a material(e.g., an unexposed, undeveloped photoresist) that may be exposed toelectromagnetic radiation (e.g., light). In semiconductor devicefabrication processes, most of the extremely small features are definedin part by use of reticles, with a large number of different reticlescorresponding to different fabrication levels, or elevations, of thesemiconductor device.

The reticles that are used in semiconductor device fabrication processestypically include a quartz substrate upon which a radiation blockinglayer is fabricated. The light blocking layer includes an opaque, ornon-transmissive, material, such as chromium. Attenuated phase shiftingreticles may also include one or more layers of partially transmissive,phase shifting materials, such as molybdenum silicide (“MoSi”) orchromium oxide (“CrO”), that phase shift radiation transmittedtherethrough (e.g., by 180°). By phase shifting the radiation,diffraction of the radiation may be reduced, improving the resolution ofthe reticle.

When the reticle is used, radiation is directed through the reticle ontoa layer of unexposed, undeveloped photoresist that has been applied to asubstrate, such as a semiconductor wafer, which transfers the patterndefined by the light blocking layer and any partially transmissiveregions to the layer of unexposed, undeveloped photoresist. The areas ofthe layer of photoresist that are exposed to radiation passing throughthe transparent areas and partially transmissive areas of the reticleare typically smaller than the corresponding transparent areas of thereticle. In some cases, the exposed areas of the photoresist havelateral dimensions that are one-fourth the sizes of their correspondinglateral dimensions of the transparent areas of the reticle.

Despite the seemingly increased tolerance that these differences indimensions may impart to a reticle during its fabrication and use, whena reticle is used in semiconductor device fabrication processes, evenvery slight damage to the reticle and the presence of very smallcontaminant particles on transparent and partially transmissiveattenuation regions of the reticle may cause imperfections in aphotoresist. These imperfections are, of course, transferred to asemiconductor device during its fabrication, and may affect theperformance and reliability of the semiconductor device and, ultimately,reduce semiconductor device yields.

One of the prevalent causes of the attraction of contaminants toreticles is the collection of electrostatic energy. The discharge ofcollected electrostatic energy, or “electrostatic discharge” or “ESD,”is also known to cause damage to the light blocking layers of reticles.ESD is particularly prevalent at the typically tapered corners 27 ofattenuation regions 26, as shown in FIG. 1. Although a number ofmeasures have been developed in an attempt to reduce the amount ofelectrostatic energy to which reticles may be exposed, they are stillexposed to some electrostatic energy, which, over time, is collected byreticle features (e.g., metallic light blocking layers).

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic representation of a portion of an embodiment of areticle according to the present invention;

FIGS. 2 through 5 depict an embodiment of a process for fabricating theembodiment of reticle shown in FIG. 1;

FIGS. 6 and 7 depict an embodiment of a process for modifying apreviously fabricated reticle of a previously existing design;

FIG. 8 is a scanning electron micrograph (SEM) of a reticle having apreviously existing design that has suffered damage from ESD;

FIG. 9 is a graph depicting a test reticle and the results that wereobtained through testing and evaluation of the test reticle forESD-induced damage;

FIGS. 10 through 12 illustrate portions of various test regions of thetest reticle of FIG. 9; and

FIG. 13 illustrates a portion of a control region of the test reticle ofFIG. 9.

DETAILED DESCRIPTION

The present invention, according to various embodiments, such as thatshown in FIG. 1, includes a reticle 10, or “photomask,” with atransparent substrate 11 (e.g., quartz), attenuation regions 26 (e.g.,MoSi, CrO) that are configured to allow some radiation to passtherethrough and to phase-shift the radiation that passes therethrough,and blocking regions 20 that comprise opaque material (e.g., chrome),which prevents the transmission of radiation. Blocking regions 20 thatinclude a plurality of discrete sections 22 that are spaced apart fromone another by way of cut lines 24. The area of each section 22, as wellas the distance across each cut line 24, or the distance that adjacentsections 22 are spaced apart from one another, minimizes or eliminatesat least one of the buildup of electrostatic energy or the discharge ofelectrostatic energy (i.e., electrostatic discharge, or “ESD”). In oneembodiment, each section 22 of each blocking region 20 has a maximumarea of about 25 μm². In another embodiment, each section of eachblocking region 20 has a maximum area of about 400 μm². While thedistance across each cut line 24 and, thus, between adjacent sections 22may be less than the resolution of reticle 10, or a “sub-resolution”distance, in some embodiments of reticle 10, the distance across eachcut line 24, or the spacing between adjacent sections 22, may be asgreat as about 0.5 μm.

Cut lines 24 may, in some embodiments, be defined along a grid withfixed lateral (i.e., x and y) distances between adjacent cut lines 24.In embodiments where cut lines 24 are evenly spaced, the areas ofsections 22 of each blocking region 20 may differ from one another, withno section 22 having an area that exceeds a predetermined maximum (e.g.,25 μm², 100 μm², 400 μm², 625 μm², 900 μm², another area that exceeds625 μm², etc.). In other embodiments, cut lines 24 may be laid out in amanner that provides each section 22 of each blocking region 20 withsubstantially the same (e.g., predetermined) surface area as one or moreother sections 22 of blocking region 20.

In some embodiments, material of attenuation regions 26 may be locatedbeneath or within cut lines 24 to prevent undesired diffusion ofradiation through cut lines 24.

The fabrication of reticle 10 may, in various embodiments, include theformation and patterning of one or more material layers on a substrate11 that comprises a material (e.g., quartz, etc.) that is substantiallytransparent to the wavelengths of radiation that will be used withreticle 10. One embodiment of such a process, in which an attenuatedphase shifting mask is formed, is illustrated by FIGS. 2 through 5.

In the illustrated embodiment, at least one layer 12 that comprises aradiation attenuating material, which blocks a known percentage ofradiation of a particular wavelength or wavelength range whilepermitting a remainder of the radiation to pass therethrough, isdisposed on substrate 11, as shown in FIG. 2. The technique by whichfirst layer 12 is disposed on substrate 11 depends at least in part uponthe material from which first layer 12 is to be formed. In someembodiments, layer 12 may comprise molybdenum silicide (“MoSi”),tantalum silicon oxyntride (TaSiON), or molybdenum silicon oxynitride(MoSiON), which may be formed by physical vapor deposition (PVD)processes.

Thereafter, as shown in FIG. 3, another layer 14 may be formed overlayer 12 and substrate 11. In some embodiments, a thickness of layer 14may be about 400 Å to about 800 Å. Layer 14 may include one or moresublayers, at least one of which includes a radiation blocking, oropaque, material. In some embodiments, the radiation blocking materialmay comprise chromium (Cr), although other known materials may also beused. In embodiments where layer 14 includes a plurality of sublayers,one of the sublayers may be formed from a material and to a thicknessthat is substantially opaque to the wavelengths of radiation with whichreticle 10 is to be used, while one or more other sublayers are formedfrom materials that will attenuate and/or phase shift the wavelengths ofradiation with which reticle 10 is to be used (with varying degrees ofattenuation if the final structure is to include more than one layer ofradiation attenuating material). The technique by which layer 14 or eachsublayer thereof is formed is appropriate for the material of that layeror sublayer. With the formation of layer 14, all of the layers of a“tritone” mask, including transparent material, attenuating material,and opaque material, are present.

In some embodiments, blocking regions 20 (FIG. 5) (i.e., a desired waferpattern) may be defined from layers 14 and 12 in a first “write,” thenblocking regions 20 (at least layer 14 thereof) may be subdivided (i.e.,cut lines 24 (FIG. 5) may be formed) in a second “write.” In otherembodiments, cut lines 24 may be formed in layer 14 as blocking regions20 are defined.

In each “writing” process, a photoresist 16 may be patterned over layer14 in the manner depicted in FIG. 4. To form photoresist 16, unexposedphotoresist may be applied to layer 14 by known techniques, such as byspin-on processes. The unexposed photoresist may then be selectivelyexposed, developed, and rinsed by known processes.

As illustrated by FIG. 5, material may be removed from regions of layer14 (FIG. 4) (or an uppermost sublayer thereof) that are exposed throughphotoresist 16 by use of suitable techniques (e.g., wet etch processes,dry etch processes, etc.) to define at least a portion of each blockingregion 20 of reticle 10, as well as cut lines 24 between discrete,spaced apart sections 22 of each blocking region 20.

Material may also be removed from underlying layers (e.g., lowersublayers of layer 14 or an underlying layer 12). Known techniques maybe effected through the same photoresist 16, through remaining portionsof a previously etched layer, with another, subsequently formedphotoresist, or with any combination of the foregoing, to removematerial from underlying layers.

In other embodiments, layer 12, 14 or sublayers thereof may be formed,then patterned, in sequence. Stated another way, each layer or sublayermay be formed, a photoresist 16 may be formed thereover, and that layeror sublayer may be etched before another layer or sublayer is formedthereover.

Regardless of the order in which processes are effected, the result isthe definition of transparent regions 28, attenuation regions 26, andopaque blocking regions 20 of reticle 10, as shown in FIG. 1.

The present invention also includes embodiments of methods for formingcut lines 24 in and defining discrete sections 22 from blocking regions20 of existing (i.e., previously fabricated) reticles. A specificembodiment of such a process includes patterning a photoresist 16′ on anexisting reticle 10′, as shown in FIG. 6, and using photoresist 16′ todefine cut lines 24 in blocking regions 20 of reticle 10′, asillustrated by FIG. 7.

With reference to FIG. 6, photoresist 16′ may be formed by applying anunexposed photoresist material to reticle 10′, exposing the unexposedphotoresist material to activating radiation, then developing theexposed photoresist material to fully cure the same. The resultingstructure includes apertures 17′ that expose portions of undividedblocking regions 20′ within which cut lines 24 (FIG. 7) are to beformed. Solid regions 18′ of photoresist 16′ cover all of the remainingareas of undivided blocking regions 20′, protecting the covered areas ofundivided blocking regions 20′ from the etchants that will be used todefine cut lines 24 in undivided blocking regions 20′.

FIG. 7 illustrates the removal of material from the exposed portions ofundivided blocking regions 20′ (FIG. 6) through photoresist 16′ todefine cut lines 24 in and subdivide blocking regions 20′ into discrete,spaced apart sections 22. Known material removal processes, including,without limitation, wet etch processes and dry etch processes employingetchants that will remove the material or materials of undividedblocking regions 20′, may be used to define cut lines 24 in undividedblocking regions 20′ and to divide at least some blocking regions 20′into a plurality of discrete, spaced apart sections 22. Once subdividedblocking regions 20 have been formed, resist 16′ may be removed and themodified reticle 10′ may be processed (e.g., cleaned, inspected,repaired if necessary, etc.) for use.

The inclusion of cut lines 24 in blocking regions 20 of a reticle 10according to embodiments of the present invention may reduce oreliminate electrostatic energy that may be built up in, and dischargedfrom, the metal (e.g., chromium) of blocking regions 20.

FIG. 8 is a scanning electron micrograph (SEM) obtained using a scanningelectron microscope available from JEOL Ltd. of Tokyo, Japan. The SEM ofFIG. 8 shows a portion of a fully fabricated reticle 10′ according to apreviously existing design, with an undivided blocking region 20′ thathas been damaged by ESD. The ESD and the damage occurred after undividedblocking region 20′ of reticle 10′ was repaired and a 25 mm² areasurrounding the repaired location was subjected to a stream of carbondioxide (CO₂) from four directions using a SCS-1100 reticle cleaningapparatus from Eco-Snow Systems of Livermore, Calif. The damage that isshown in FIG. 8 surrounds the location of undivided blocking region 20′that was repaired, and is theorized to have been caused as the highvelocity stream of CO₂ from the SCS-1100 reticle cleaning apparatuscaused electrostatic energy stored within undivided blocking region 20′to discharge from undivided blocking region 20′ during apost-fabrication inspection, repair, and clean of reticle 10′.

This theory was tested by fabricating a test reticle 10″ of the sametype as that shown in FIG. 8, with an experimental half 30 (the lefthalf) and a control half 50 (the right half). Test reticle 10″ isdepicted by FIG. 9 in the form of a graph. Experimental half 30 includedthree experimental areas 35, 40, and 45. In the uppermost (as thedrawing sheet is oriented) experimental area 35, blocking regions 20 oftest reticle 10″ were divided into discrete, spaced apart sections 22(FIG. 1) by way of 0.5 μm wide cut lines 24 (FIG. 1) that were organizedin a grid and spaced apart 15 μm apart from one another (i.e., cut lines24 were organized as a 15 μm×15 μm square grid) (see also FIG. 10).Blocking regions 20 of a center experimental area 40 were divided intodiscrete, spaced apart sections 22 by way of 0.5 μm wide cut lines 24that had been organized as a 10 μm×10 μm square grid (i.e., verticallyextending cut lines 24 were spaced 10 μm apart from each other, andhorizontally extending cut lines 24 were spaced 10 μm apart from eachother (see FIG. 11). A lowermost experimental area 45 of experimentalhalf 30 of test reticle 10″ included 0.5 μm wide cut lines 24 that wereorganized as a 5 μm×5 μm square grid to divide blocking regions 20within experimental area 45 into discrete, spaced apart sections 22having maximum surface areas of 25 μm² (see FIG. 12). While thedistances between the cut lines 24 appear to be about the same in eachof FIGS. 10 through 12, it is notable that the blocking regions 20 overwhich they are formed have the same widths, which appear to bedecreasingly smaller from FIG. 10 through FIG. 12. Blocking regions 20′of control half 50 remained undivided, as depicted in FIG. 13.

As reticle inspection processes are typically effected at numerouspoints throughout reticle fabrication processes, three test locations 32on experimental half 30 of reticle 10″ and three corresponding testlocations 52 on control half 50 of test reticle 10″ were subjected to ahigh velocity stream of CO₂ from the SCS-1100 reticle cleaning apparatusduring an intermediate point in the process of fabricating test reticle10″. The high velocity stream of CO₂ was directed toward eachpreselected test location 32, 52 from four different directions, whichwere oriented at 90° intervals around each preselected test location 32,52, onto a 5 mm² area centered about that preselected test location 32,52.

Upon inspecting test reticle 10″ with defect inspection equipmentavailable from KLA-Tencor Corporation of San Jose, Calif., someESD-induced damage was detected, albeit significantly less than thedamage illustrated in FIG. 8, which occurred after reticle 10′ had beencompletely fabricated, repaired, and cleaned.

Once fabrication of test reticle 10″ was complete, the SCS-1100 reticlecleaning apparatus was again used, this time to direct a high velocitystream of CO₂ toward five different preselected test locations 37, 42,47 in each area 35, 40, 45, respectively, of experimental half 30 ofreticle 10″ and toward fifteen different preselected test locations 57across control half 50 of reticle 10″. Again, the high velocity streamof CO₂ was directed toward each preselected test locations 37, 42, 47,57 from four different directions, which were oriented at 90° intervalsaround each preselected test location 37, 42, 47, 57, onto a 5 mm² areacentered about that preselected test location 37, 42, 47, 57.

Thereafter, a 125 nm resolution inspection of test reticle 10″ wasconducted using the KLA-Tencor defect inspection equipment. In thatinspection, the features of the test reticle 10″ that were visualized bythe defect inspection equipment were compared with the intended featuresof test reticle 10″ (i.e., the data that were used to controlfabrication of test reticle 10″) to identify the locations of all of thedefects and irregularities of test reticle 10″. Each location in which adefect was identified, or “defect location,” was then visually inspectedusing a JEOL scanning electron microscope. Visual inspection of testreticle 10″ was conducted blindly, i.e., without informing theinspectors of any of the preselected test locations 32, 52, 37, 42, 47,57 or of the locations where blocking regions 20 (FIG. 1) had beensubdivided into discrete, spaced apart sections 22.

The results of the evaluation of test reticle 10″ are set forth in thegraph of FIG. 9. Notably, there are several times more defect locations60 on control half 50 of test reticle 10″ than appear on experimentalhalf 30 of test reticle 10″. Most of the defects on control half 50 wereconcentrated at or near preselected locations 57 on control half 50,while there was no distinctive concentration of defect locations 60 atany preselected location 37, 42, 47 on experimental half 30. Visualinspection of the SEMs of defect locations 60 on control half 50revealed that many of the defects located by the defect inspectionequipment were damage caused by ESD, while visual inspection of defectlocations 60 on experimental half 30 showed no ESD-induced damage.

Further analysis was conducted to verify the absence of ESD-induceddamage to preselected test locations 37, 42, and 47 on experimental half30 of test reticle 10″. Again using the scanning electron microscope, asecond visual inspection was conducted on each defect location 60 onexperimental half 30. Subsequent inspections for ESD-induced damage andother anomalies of unknown causes identified no such defects or damage.With the assistance of the scanning electron microscope at a highermagnification (i.e., 10,000× and 70,000×), a third visual inspection ofthese same defect locations was conducted. The third visual inspectionconfirmed the absence of ESD-induced damage on experimental half 30 oftest reticle 10″.

Visual inspection of test reticle 10″ further confirmed that thehorizontal bands of defect locations 60 that extend across experimentalhalf 30 were from the rounding of the corners of blocking regions 20 orunderlying attenuation regions 26, which occurred as material layerswere etched to form blocking regions 20 and/or attenuation regions 26.

These results indicate that the subdivision of blocking regions 20 of areticle 10 reduces or eliminates the likelihood that electrostaticenergy will be discharged from blocking regions 20, as well as thelikelihood of damage that would have otherwise been caused by such ESD.It is also believed that the subdivision of blocking regions 20minimizes or eliminates the storage of electrostatic energy by blockingregions 20.

Use of a reticle 10 according to embodiments of the present inventionmay avoid a number of problems associated when undivided blockingregions 20′ of existing reticles 10′ become charged with electrostaticenergy. Such uses may be effected alone or in combination with otherstatic suppression techniques or features. One embodiment of use of areticle 10 according to the present invention includes the reduction orelimination of damage that may be caused by the buildup or discharge ofelectrostatic energy. The likelihood and magnitude of ESD damage causedduring post-repair cleaning may be reduced or eliminated.

In another embodiment, use of a reticle 10 of the present invention mayreduce or eliminate the electrostatic attraction and adhesion ofcontaminants to reticle 10, along with the incidence of semiconductordevice defects attributable to such contamination. As such, use of areticle 10 according to an embodiment of the present invention insemiconductor device fabrication processes will result in semiconductordevices of increased reliability and increase semiconductor deviceyields.

Although the foregoing description contains many specifics, these shouldnot be construed as limiting the scope of the present invention, butmerely as providing illustrations of some embodiments. Similarly, otherembodiments of the invention may be devised which lie within the scopeof the present invention. Features from different embodiments may beemployed in combination. The scope of the invention is, therefore,indicated and limited only by the appended claims and their legalequivalents, rather than by the foregoing description. All additions,deletions and modifications to the invention as disclosed herein whichfall within the meaning and scope of the claims are to be embracedthereby.

1. A reticle, comprising: a radiation blocking material over a surfaceof a transparent substrate, the radiation blocking material includingdiscrete sections, each discrete section having a sufficiently smallsurface area to minimize at least one of electrostatic buildup on andelectrostatic discharge from the radiation blocking material, adjacentdiscrete sections of the radiation blocking material separated from oneanother by a subresolution distance.
 2. The reticle of claim 1, whereinthe discrete sections are arranged in a grid array.
 3. The reticle ofclaim 1, wherein each discrete section has a maximum surface area ofabout 900 μm².
 4. The reticle of claim 1, wherein each discrete sectionhas a maximum surface area of about 400 μm².
 5. The reticle of claim 1,wherein the adjacent discrete sections of the radiation blockingmaterial are separated from one another a distance sufficient to inhibitelectromagnetic radiation from being transmitted between the adjacentdiscrete sections.
 6. The reticle of claim 1, wherein the adjacentdiscrete sections of the radiation blocking material are spaced adistance of about 0.5 μm apart from each other.
 7. A reticle,comprising: a radiation blocking material over a surface of atransparent substrate, the radiation blocking material comprisingdiscrete sections, adjacent discrete sections of the radiation blockingmaterial separated by a space of subresolution width.
 8. The reticle ofclaim 7, wherein each discrete section is of a surface area selected tominimize at least one of buildup of electrostatic energy and dischargeof electrostatic energy.
 9. The reticle of claim 7, further comprising aradiation attenuation material within the space.
 10. The reticle ofclaim 1, wherein the discrete sections have the same surface area. 11.The reticle of claim 1, wherein the discrete sections have differentsurface areas.
 12. The reticle of claim 7, wherein the radiationblocking material comprises chromium.
 13. The reticle of claim 7,wherein the radiation blocking material comprises a plurality ofsublayers.
 14. The reticle of claim 13, wherein one sublayer of theplurality of sublayers comprises a substantially opaque material. 15.The reticle of claim 13, wherein at least one sublayer of the pluralityof sublayers comprises a phaseshift material.